The invention relates to a switchable planetary gearbox, in particular, for a hand-held power tool, comprising a planetary carrier supporting on one end face several planet wheels whose toothing meshes permanently with a sun wheel toothing of a central rotary sleeve. The planetary gearbox further comprises a switching ring gear surrounding the planet wheels and meshing permanently with the toothing of the planet wheels. The switching ring gear is longitudinally slidable and, for switching a transmission stage of the planetary gearbox, can be moved into engagement with an outer circumferential toothing that is provided on the circumference of a radial section of the rotary sleeve covering the end face of the planet wheels facing away from the planetary carrier.
As is known in the art, planetary gearboxes are comprised essentially of a central sun wheel on which the planet wheels supported on a planetary carrier are rolling. Usually three planet gear wheels are supported externally on the concentrically arranged ring gear. Such a gearbox is suitable, in particular, for use in hand-head working tools such as power drills because the configuration of the planetary gearbox provides a favorable ratio between size and transmittable power for a relatively high possible transmission ratio.
German patent DE 42 13 291 C2 discloses a planetary gearbox for a hand-held hammer drill wherein the gearbox acts by means of a crown gear onto the drive spindle of the drill. In order to be able to shift into the different gears of the hammer drill, the planetary gear is provided with different transmission stages wherein shifting between the stages is realized by means of an axially movable switching ring gear moveable into several displacement positions. One of the transmission stages of the gearbox corresponds to a position of the switching ring gear in which the switching ring gear is blocked by a locking member that is provided on the housing of the gearbox and engages the toothing of the switching ring gear for blocking. By axial movement of the partial switching ring gear by means of a gear shifting grip, the transmission stage can be switched in that the toothing of the switching ring gear is moved into engagement with the outer toothing of a gear member that covers the planet wheels radially. In the known planetary gearbox, the radial section supporting the outer toothing is provided on the central sleeve that supports the sun wheel toothing or is kinematically coupled therewith.
On the planetary gearbox of the power tools, usually an increased wear is observed during operation of the power tool and this wear is worsened even more by repeated shifting during operation when idling or operating under load. Particularly the inner toothing of the switching ring gear and the outer toothing of the web that is to switched or blocked are subject to the wear effects.